function $ajax({
    url,
    success
}){
    var xhr = new XMLHttpRequest();
        xhr.open('get',url,true)
        xhr.send();
        xhr.onreadystatechange = function(){
            if(xhr.readyState===4&&xhr.status>=200&&xhr.status<300){
                var res = JSON.parse(xhr.responseText)
                success(res);
            }
        }
}